Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B23/00—Obtaining nickel or cobalt
  • C22B23/04—Obtaining nickel or cobalt by wet processes
  • C22B23/0453—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B23/0461—Treatment or purification of solutions, e.g. obtained by leaching by chemical methods
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
  • B22F9/20—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds
  • B22F9/22—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds using gaseous reductors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/06—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder
  • H01F1/061—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder with a protective layer

Definitions

• This invention relates to the production of finely divided metal powders and, more particularly, to a process for the production of finely divided cobalt powders.
• the invention is also concerned, in its more specific aspects, with certain ultra fine magnetic cobalt powder products obtainable by the process.
• cobalt powders there are various uses in industry for very finely divided cobalt powders including, for example, production of sintered carbide products, such as metal stamping and cutting tools. Certain kinds of fine cobalt powder also find application in the manufacture of devices incorporating fine particles of magnetic materials such as magnetic tapes and ink and permanent magnets to mention only a few.
• the basic requirements for cobalt powder for use in sintered carbides production are fine particle size, i.e. less than 2 microns and preferably about 1 micron, and high purity. Oxygen content must be less than 1 wt. %, preferably about 0.5 wt. % or less, and carbon content must be less than 0.2 wt. %.
• the physical requirements for magnetic cobalt powders are similar except that smaller particle size, e.g. about 0.8 micron or less is preferred, and oxygen content may be slightly higher, e.g. up to about 2 wt. %.
• the present invention provides a surprisingly simple, economic and flexible process for producing a variety of fine and ulra fine cobalt powders.
• fine as applied to particle size is intended to mean particles in the 1 to 2 micron size range.
• Ultra fine is intended to mean particles about 1 micron and smaller in size).
• the process is equally adaptable for producing fine cobalt powders for use in the sintered carbides field or ultra fine powders particularly adapted for magnetic applications as well as for other powder metallurgy applications where small particle size is a necessary requirement of the powder.
• fine and ultra fine cobalt powders are produced by a process involving two basic operations. Firstly, finely divided cobaltous carbonate is prepared by precipitation from a cobaltous ammine-ammonium sulphate solution by reacting the solution with carbon dioxide under conditions which are specifically controlled to control the particle size of the cobaltous carbonate precipitate. Secondly, the cobalt carbonate precipitate is separated from the solution and is dry-reduced with hydrogen under controlled conditions of time and temperature to produce finely divided elemental cobalt powder.
• the process of the invention includes the steps of providing an aqueous cobaltous ammine-ammonium sulphate solution having a free ammonia to cobalt molar ratio of at least about 2.0; heating said solution in a closed reaction vessel to a temperature within the range of about 50° C. to about 120° C.; actively agitating said heated solution and reacting it with carbon dioxide under a partial pressure of carbon dioxide within the range of from about 20 p.s.i. to about 300 p.s.i.
• ultra fine cobalt particles are produced by depositing a small quantity of a refractory oxide forming compound, such as magnesium hydroxide or yttrium hydroxide, on the particles of cobaltous carbonate precipitate prior to the reduction with hydrogen.
• a refractory oxide forming compound such as magnesium hydroxide or yttrium hydroxide
• this compound functions to prevent migration of cobalt atoms during heating thus inhibiting the growth of the cobalt particles.
• the refractory metal compound Upon exposure to air after cooling, the refractory metal compound is converted to sub-micron refractory oxide particles.
• a powder product obtainably by this procedure consists of non-pyrophoric magnetic particles of cobalt of a size predominantly no larger than about 1 micron and preferably no larger than a single magnetic domain (0.8 micron).
• the cobalt particles have a minor amount of refractory oxide particles fixed in the surfaces thereof which serve to stabilize the powder, permitting handling and substantially preventing spontaneous oxidation of the particles on exposure to air such that the oxygen content of the powder (excluding that associated with the refractory oxide particles) remains substantially unchanged.
• a further preferred modification of the process contemplates the grinding of the CoCO 3 precipitate, such as by wet ball milling, prior to the reduction step as a means of further decreasing the particle size of the precipitate.
• the first requirement is the provision of an aqueous cobaltous amine-ammonium sulphate solution.
• aqueous cobaltous amine-ammonium sulphate solution may already be available in commercial cobalt production plants which utilize hydrometallurgical cobalt recovery processes such as that described in U.S. Pat. No. 2,767,054, for example.
• Such solution may also be made up by dissolving cobaltous ammonium sulphate salt or metallic cobalt in ammonia-ammonium sulphate solution, or by dissolving cobalt oxide or metallic cobalt in H 2 SO 4 .
• cobalt in the feed solution it is essential to the operation of the process that the cobalt in the feed solution be in the cobaltous form. Any cobaltic cobalt in the feed solution will not be precipitated in the subsequent steps of the process so that the yield of precipiate will decrease in direct proportion to the amount of cobalt present in the cobaltic form.
• the specific quantity of cobalt in the solution is not critical to the operation of the process. In general, the process is operable with any amount of cobalt up to its limit of solubility in the solution. However, for practical economic and operating reasons, a cobalt concentration of about 40-70 g.p.l. is preferred.
• a concentration of 40-45 g.p.l. is most preferred in that with concentrations above about 45 g.p.l., the ammonium sulphate concentration must be very high, e.g. 500 g.p.l. or more to keep the cobalt in solution and such high (NH 4 ) 2 SO 4 concentrations tend to increase the amount of sulphur contamination in the precipitate.
• the cobaltous ammine-ammonium sulphate solution is reacted in an agitator equipped pressure vessel with carbon dioxide at a temperature within the range of about 50° C, to about 120° C., preferably about 75°-100° C., under a carbon dioxide partial pressure within the range of about 20 p.s.i. to about 300 p.s.i., preferably about 50-100 p.s.i., to form and precipitate cobaltous carbonate.
• the upper carbon dioxide partial pressure limit is not critical to the operation of the process but is determined by equipment considerations.
• the upper and lower temperature limits and the lower CO 2 partial pressure limit define the range within which a reasonable yield of precipitate is obtained from the reaction. The yield, i.e.
• percent of total dissolved cobalt precipitated from the feed solution, and the particle size of the CoCO 3 precipitate are functions of the feed solution composition and other process variables, including mainly temperature, CO 2 partial pressure, reaction time and degree of agitation. Because of the large number of variables and the apparent interdependence of these variables, it is not possible to isolate the effect of each variable. However, it has been found that through appropriate control and correlation of the principal variables, both high yield and close control over the particle size of the cobaltous carbonate preciptitate can be obtained. Since the fineness of the cobalt powder product is directly related to the fineness of the cobaltous carbonate precipitate, this control of precipitate particle size permits control of the particle size of the cobalt powder product.
• a wide range of free ammonia (NH 3F ) to cobalt molar ratios may be used in the feed solution for the CoCO 3 precipitation step with little or no adverse affect on the yield or physical properties of the preciptitate provided other conditions are appropriately adjusted.
• Free ammonia means ammonia in the system which is titratable with H 2 SO 4 ). More specifically, with any NH 3F /Co molar ratio above about 2, at least a 60% yield of CoCO 3 precipitate having a Fisher number below about 1.0 is obtained with any CO 2 partial pressure and temperature within the aforementioned general ranges.
• NH 3F /Co molar ratio should be in the range of 2-4.5. NH 3F /Co molar ratios at the higher end of this range are preferable in that less impurities, particularly sulphur, precipitates with the CoCO 3 at these conditions. There is no upper limit on the NH 3F /Co molar ratio insofar as operability of the process is concerned, but from a practical point of view, there is really no purpose in going beyond a NH 3F /Co molar ratio of about 6 since there is no beneficial effect obtained with such higher ratios.
• the pecipitate Upon completion of the CoCO 3 precipitation reaction the pecipitate is separated from the precipitation-end solution. In order to remove ammonium sulphate, and hence sulphur that crystallizes on the cobalt carbonate precipitate when discharging the reaction vessel, it is preferred to wash the precipitate with fresh water. If the precipitate is not washed, sulphur in the crystallized ammonium sulphate may report as an impurity in the cobalt powder after solid state reduction.
• the washed CoCO 3 precipitate may next be passed directly to the reduction operation which is described in greater detail hereinbelow or it may be slurried with water and wet ball milled for a period of time, e.g. 3-6 hours, to further decrease the size of the precipitate particles.
• a period of time e.g. 3-6 hours
• ball milling will only be required if, for some reason, the desired degree of fineness cannot be obtained through control of precipitation conditions alone.
• the CoCO 3 precipitate may, prior to the reduction operation, be treated in an additional step or steps to deposit on the precipitate particles a refractory oxide forming metal compound which functions to prevent sintering and growth of particle size in the reduction operation.
• This modification of the process permits the production of ultra fine cobalt powders which are stable under atmospheric conditions and which have particularly useful magnetic properties.
• a preferred procedure for deposition of the refractory metal oxide forming compound is to first disperse the CoCO 3 from the precipitation step in water containing ions of a refractory oxide forming metal such as Mg, Ca, Ba, Al, Be, Ce, Hf, La, Th, Y and Zr.
• a refractory oxide forming metal such as Mg, Ca, Ba, Al, Be, Ce, Hf, La, Th, Y and Zr.
• Ions of the refractory oxide-forming metal or metals may be introduced into the suspending medium in a number of ways.
• a soluble salt such as magnesium, calcium or barium sulphate or yttrium or thorium nitrate may be dissolved in an aqueous solution and the solution added to the CoCO 3 slurry.
• the pH of the slurry is then adjusted by the addition of a base to cause the refractory metal to precipitate onto the suspended CoCO 3 particles.
• the pH is adjusted to about 8.5-9.5 by addition of ammonia.
• the slurry may be agitated and with agitation the reaction is usually complete inless than 15 minutes.
• the concentration of refractory oxide-forming metal ions in the solution is governed by the amount of refractory oxide-forming compound (sometimes hereinafter abbreviated as ROF) which is desired on the CoCO 3 particles.
• the concentration of any given refractory oxide-forming metal which will deposit the desired amount of ROF compound can be calculated having regard to the CoCO 3 content of the slurry.
• the precise amount of deposited ROF compound is not of particular importance to the overall operativeness of the process. However, since the quantity of deposited ROF compound has a pronounced affect on the particle size of the cobalt powder product, the quantity must be selected having regard to particle size that is desired.
• the minimum amount of ROF compound that will be effective to give the degree of particle size control that is desired.
• the amount can be readily determined in each specific case by a few routine experimental tests. In most cases, the desired effect will be obtained in an amount of refractory oxide forming metal compound sufficient to provide from about 0.1 to about 6 wt. % of the corresponding refractory oxide in the final cobalt powder product.
• the fineness of the final product increases with increase of refractory oxide content.
• the preferred cobalt powder particle size for a particular magnetic application may not necessarily be the absolute minimum that is obtainable by the process, the optimum refractory oxide content may vary for each case depending on the circumstances applicable.
• the slurry may be passed to a liquids-solids separation step for the recovery of the CoCO 3 precipitate or, optionally, before separation of the CoCO 3 the slurry may be treated in a grinding or ball milling operation to further decrease the article size of the CoCO 3 --ROF compound precipitate.
• a grinding or ball milling operation may be utilized in any case where it is desired to further decrease the particle size of the CoCO 3 precipitate. In most cases where further grinding is used, about 4-6 hours of wet ball milling will be sufficient to lower the Fisher number of a relatively coarse CoCO 3 precipitate to below about 1.
• the CoCO 3 precipitates is next heated at an elevated temperature in a hydrogen atmosphere to convert the CoCO 3 to pure elemental cobalt powder.
• the reduction reaction can be carried out in any suitable kiln or furnace in which the temperature and atmosphere can be controlled to provide the conditions necessary for reduction of the CoCO 3 to elemental cobalt powder.
• it is essential to maintain the temperature of the CoCO 3 within the range of about 400° C. to about 700° C. with the precise temperature depending on the quantity of refractory oxide forming compound associated with the CoCO 3 and the degree of fineness desired for the final product.
• the reducing temperature preferably should be maintained between about 400°-600° C. and, if maximum fineness is desired, at about 550° C. With higher amounts of refractory oxide forming compound somewhat higher temperatures, e.g. up to 650° C., can be utilized without adversely affecting the particle size of the final product.
• the precise time required for the complete reduction of the CoCO 3 will depend on the temperature. In any case, the reduction step must be continued for a sufficient time to lower the residual oxygen content (exclusive of oxygen associated with the refractory oxide forming compound) to less than about 2.0% and, if required by product specification, to less than 0.6% by wt. %. In most cases, 3-6 hours is sufficient time for the reduction step.
• the higher the refractory oxide forming compound content of the CoCO 3 the higher the reduction temperatures and the shorter the reduction times that can be employed.
• the hot reduced cobalt particles oxidize extremely rapidly on exposure to air. To avoid spontaneous combustion of the particles, they must be cooled in a non-oxidizing atmosphere, such as nitrogen, before exposure to the atmosphere.
• a non-oxidizing atmosphere such as nitrogen
• the degree of cooling required before exposure to the atmosphere depends on the presence or absence of the refractory oxide forming compound.
• the cobalt powder In the case of Co powder containing no refractory oxide forming compound, the cobalt powder must be cooled at least to room temperature before exposure to air. Preferably such powders are cooled to 5°-10° C. below room temperature before exposure to air. Upon exposure to the air, such particles are stable and non-pyrophoric.
• Co particles having the refractory oxide forming deposit thereon it is desirable but not essential to cool the particles under non-oxidizing conditions to room temperature before exposure to air. However, in most cases, cooling to within about 100° C. of room temperature is sufficient.
• the deposited compound of the refractory oxide forming metal decomposes to a refractory oxide which remains fixed on the surfaces of the cobalt powder as sub-micron sized particles. This refractory oxide serves to stabilize the cobalt powder product, preventing incipient spontaneous oxidation of the powder during handling, storage and use.
• the preferred product powders obtained by this modification of the process are composed of extremely fine, magnetic cobalt particles having sub-micron sized refractory oxide particles fixed on the surfaces thereof and containing less than 2% oxygen (exclusive of the oxygen associated with the refractory oxide) and having a particle size no larger than a single magnetic domain, i.e. no larger than 0.8 micron.
• These powders have a coercivity of 200-400 oersteds and a remanent induction value of 2000-7000 gauss, making them suitable for magnetic applications wherein this combination of relatively high coercivity and remanence are desired.
• This example illustrates the affect of various processes variables on the particle size of the CoCO 3 produced in the precipitation step of this process.
• the feed solution for the tests was prepared by dissolving cobaltous ammonium sulphate salt in aqueous ammonia-ammonium sulfate solution. After appropriate adjustment of the composition, 2 liter samples of solution were charged into a one gallon high pressure laboratory autoclave, heated to operating temperature and reacted with CO 2 under pressure. After completion of each test run, the CoCO 3 precipitate was separated from the remaining solution by filtration and subjected to washing in order to remove sulphur contamination.
• This sample illustrates the preparation of ultra fine magnetic cobalt powder containing a small amount of refractory oxide forming compound.
• Cobaltous carbonate was precipitated from cobaltous ammine sulphate solution as described in Example II.
• the cobalt carbonate was separated from the liquid and was divided into a number of samples. Each sample was dispersed in 220 ml water amd to each was added a calculated quantity of a yttrium nitrate solution to produce slurry samples containing the equivalent of from 0 to 0.33 mols yttria per 100 g. cobalt.
• the yttrium nitrate solution as prepared by dissolving commercially available yttrium in nitric acid at a temperature of 95° C.
• the composition of the solution was 2 moles per liter Y + + + + and 6 moles per liter NO 3 - .
• a sample of cobalt powder was prepared in the same way as that described in Example 4 except that thorium nitrate was used in place of yttrium nitrate.
• the properties of the powder product were: Thoria content -- 2.7 wt. %, Fisher number -- 0.64, coercivity -- 200 oersteds, residual magnetization value -- 2550 gauss.

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Citations (9)

• 1973
  • 1973-03-30 GB GB1552273A patent/GB1436595A/en not_active Expired
• 1974
  • 1974-02-01 CA CA191,532A patent/CA1013595A/en not_active Expired
  • 1974-03-19 PH PH15636A patent/PH10513A/en unknown
  • 1974-03-20 ZA ZA00741828A patent/ZA741828B/xx unknown
  • 1974-03-26 AU AU67139/74A patent/AU475404B2/en not_active Expired
  • 1974-03-26 FI FI915/74A patent/FI66435C/fi active
  • 1974-03-28 FR FR7410885A patent/FR2223119B1/fr not_active Expired
  • 1974-03-28 JP JP3402374A patent/JPS5722963B2/ja not_active Expired
  • 1974-03-29 DE DE2415442A patent/DE2415442A1/de not_active Ceased
  • 1974-03-29 US US05/456,482 patent/US3994716A/en not_active Expired - Lifetime
  • 1974-03-29 BE BE142644A patent/BE813057A/xx not_active IP Right Cessation
• 1975
  • 1975-11-26 PH PH17806A patent/PH11716A/en unknown

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